Insects and Parasitic Diseases. 79 



Professor W. B. Heiiiis refers briefly to the Louse-fly, remarking 

 lliat when, off the sheep the insects die in from two to eight days. 



The investigations made by Dr. Georgina Sweet and Mr. H. R. 

 Redden, B.Y.Sc. (1917) dealt with one aspect of the subject, namely, 

 the viability of the sheep Louse-fly when removed from the host. 

 These authors refer to the statements of earlier investigators and 

 authors as showing that the life of the parasite oft' the liost and 

 •deprived of its food is generally believed to be from two to seven 

 days. They were unable to find any record of sheep Louse-flies 

 being kept alive under th,ese conditions to the eighth day. Their 

 own investigations, which are recorded in detail, showed that 

 under certain conditions the Louse-fly lived for varying periods 

 up to eleven and three-quarter days off the host and without food. 

 The condition found to be most favourable was the moderately cool, 

 uniform temperature of a cellar. Tavo groups of insects were kept 

 under such conditions, one group on bare soil and the other on 

 soil on which rested a few dry leaves. The first group were all dead 

 in eleven days, whilst the second group Avere all dead in eleven and 

 three-quarter days. At the same time another group was kept on 

 wool in the cellar; these were all dead in four days. In one experi- 

 ment in early December (sunnner), a group of Louse-flies was placed 

 on a moist sod of lawn grass out of doors; these Avere all dead in 

 five and three-quarter days. In tAvo other experiments out of 

 'doors, all the insects died in tAvo and three-quarter days. 



1. Experiments to determine the incubation period of the pupae. 



Experimenf No. 1. 



Eleven pupae extruded during the preceding tAA^elve hours Avere 

 placed (May 30th) in a small muslin bag secured to the fleece on a 

 -sheep's back, \ in. to \ in. from the skin and 2 J in. to 3 in. from 

 the surface of tlie avooI, the sheep being housed in a brick stall, in 

 which the temperature ranged during the experiment from 45°F. 

 to 47°F. Tavo young Louse-flies emerged on the twenty-second day, 

 three on tlie tAventy-thiid day, and three on the 24tli day. Three 

 pupae failed to produce young. 



Erperimeni No. 2. 



TAvelve pupae extruded between 2 p.m. on Septeml)er lOtli and 5 

 p.m. on September 11th (early spring), by females enclosed Avithin 

 -a small area of avooI on a sheep's back, produced four young flies on 



